1. Field of the Invention
The present invention is directed to a process and apparatus for displaying an image in front of an optically contrasting background by means of a display installation or device which has a plate-shaped body, which traps ambient light and emits it through exit windows, and has a light valve associated with each of the exit windows which is controllable to determine whether the light emitted from the exit windows is blocked or allowed to pass through the valve.
2. Prior Art
The use of image brightening fluorescent plates in a display which displays are also called fluorescent activated displays (FLAD) are known and have been described in U.S. patent application Ser. No. 747,035 filed Dec. 2, 1976 which issued as U.S. Pat. No. 4,142,781 and incorporates the disclosure of German Offenlegungsschrift No. 2,554,266. Also, such devices have been described in an article entitled "Bright and Economical", Electronics Newspaper, Mar. 25, 1977 and in an article in Electronics 6, (1977), page 55. The fluorescent plates discussed in the above mentioned references collects the bulk of the ambient light striking it by means of fluorescent absorption and emission with subsequent total reflection at its interfaces. The emitted fluorescent light is conducted in the interior of the plate and subsequently emitted through the special light exit or delivery windows, which may be created by roughening of the selected surface area or by the provision of notches. When a display unit with the display element aligned with each light delivery or exit window is located in front of such a plate, the luminous strength of the image display is increased by a factor which approximately corresponds to the ratio between the area of the light collecting surface of the plate and the area of the light emitting exit windows. In previously known FLAD devices, a field effect liquid crystal display with a twisted liquid crystal layer, for example, a rotary cell liquid crystal such as described in German Offenlegungsschrift No. 2,158,563, was provided as the light valve. Such a display, which utilizes the rotary cell has certain disadvantages, for example, a rotary cell has only a limited viewing angle zone, does not provide contrast gradations without substantial modifications and is supposed to be operated with a pure alternating voltage which can only be provided with extreme difficulties, particularly in a multiplex operation or mode which is increasingly being desired. It must be further noted that the manufacture of a rotary cell still demands special care and thus the mass production of displays utilizing rotary cells have not yet been completely successful.